This invention relates generally to correcting appearance variations in production-scale molded plastic parts, and specifically to using a laboratory-scale tool to duplicate streaking defects seen in production-scale parts and measuring and analyzing these defects so they can be corrected in subsequent production runs.
Consumers of durable plastic products ranging from toys to computer and printer housings to vehicles expect a uniform surface finish with no visible flaws, streaks, or defects. Common defects include streaks where various plastic flows meet in a part. These streaks may arise as different flow fronts from different gates meet or downstream of flow disruptions such as grills, bosses, ribs, or holes.
Currently, few, if any, numerical specifications related to uniformity of appearance are given to a supplier of raw plastic products outside of average color and possibly gloss or haze. Nevertheless, the molder creating the part and the consumer each expect a product with no visible flaws. The consumer, in particular, may view appearance defects as both unsightly and as indicative of poor quality material that will not last for long term use.
Currently, the quality, uniformity, and lack of defects in a part is typically judged solely using visual inspection on production parts. This leads to an absence of numerical specifications, lack of consistency due to operator variation, and an inability to consistently and rapidly process a large number of samples. Further, a large amount of waste may be generated since a large number of defective parts must be molded to attempt to quantify the problem. Often, the molder or customer is unable to transmit a complaint to the plastic supplier that is more specific than xe2x80x9ca streaking problem exists,xe2x80x9d and many pounds of rejected production parts are shipped back to the plastic supplier for subsequent visual evaluation. Yet, it is difficult for the supplier to address the problem and provide solutions in the absence of effective measurement tools.
Several prior commonly-assigned and invented patents and patent applications, namely, U.S. Pat. No. 5,859,708, issued Jan. 12, 1999; and U.S. application Ser. Nos. 09/075,913; 09/188,094; and 09/188,095; address vagaries of visual inspection via a spatially resolved spectrometer which can resolve small defects which are not apparent to a standard spectrometer with the typical xc2xd inch diameter or larger aperture. Further, unlike the few spectrometers capable of smaller apertures which are not automated, the spectrometer described earlier may be interfaced with a computer for motorized sample movement and automatic data collection.
Commonly-assigned and invented U.S. patent application Ser. No. 09/303,409 discloses how to perform automated inspection of complex, curved, or textured parts, and how to process and quantify the massive amount of data generated by the spatially-resolved spectrometer of the above-references disclosures.
But, improving performance in production is still largely a xe2x80x9chit or missxe2x80x9d proposition, without quantitative information to guide the manufacturer.
Accordingly, there is a need in the art for a system and method to correct production defects by screening different resin formulations for streaking performance and to define processing windows which yield acceptable performance.
Using the molding tool, spatially-resolved spectrometer and computerized device of U.S. patent application Ser. No. 09/303,409, streaking problems identified in production are first duplicated on a laboratory scale. Next, options are developed for fixing (correcting) the observed problem and testing these on a laboratory scale. Finally, the option(s) chosen for correcting the observed problem are validated prior to reinitiating full-scale production.
Whereas the disclosure of U.S. Ser. No. 09/303,409 focuses on a molding tool, spatially-resolved spectrometer and computerized device and using these to establish appropriate resin formulations and processing conditions for a given production run with certain desired characteristics, the instant disclosure focuses on using the molding tool, spatially-resolved spectrometer and computerized device of U.S. Ser. No. 09/303,409 to analyze and correct preexisting production defects.